1. Technical Field
This invention relates to a method for the synthesis of composite oxides by an improved citrating process.
2. Background Art
Generally, citrate forming processes are applied in forming particles of functional ceramic materials utilized in such as magnetic substances, catalysts, sensors, superconductors, dielectric substances and optical materials.
C. Marcilly et al. in the Journal of the American Ceramic Soc., 53, 56 (1970) discloses a method for synthesizing a composite oxide by mixing citric acid with nitrates and/or acetates of metals. Recently, Hirabayasi et al. in the Journal of Japan Inst., metals, 26, 10 (1987) discloses a method for synthesizing a composite oxide having superconductivity at high temperatures by mixing nitrates of Y, Ba and/or Cu with citric acid and ethylene glycol.
However, these methods for forming citrates are methods whereby citric acid is merely added to an aqueous solution of nitrates and/or acetates. Furthermore, as added citrates are merely dissolved, metallic nitrates and/or metallic acetates and citrates coexist in the solution. In this stage, citrates are not formed. Citrates are obtained after heating and condensing this solution and dehydrating. However, this procedure causes great amounts of poisonous gases such as nitric acid (HNO.sub.3), nitrogen oxide (NO.sub.x), acetic acid (CH.sub.3 COOH) to be found.
Furthermore, after dehydration, gelated citrate adheres strongly and viscidly to its container, this causes difficulty in treating and decreases the overall yield.
Moreover, when baking citrate, it forms an oily compound and burns fiercely with much black smoke, which is very dangerous. This caramel-like compound bulges out at high temperatures and causes difficulty in finishing the baking.
Thus, the above mentioned prior art has many problems in both the pollution and system aspects when applied industrially.
It is therefore an object of this invention to provide a method for synthesizing a composite oxide which produces no poisonous gases during the procedure.
It is another object of this invention to provide a method for synthesizing a composite oxide which can obtain high yields.
It is further object of this invention to provide a method for synthesizing a composite oxide having homogeneity and high quality.
It is additional object of this invention to provide a method for synthesizing a composite oxide which can be established for mass productive industrialization.